1. Field of the Invention
The present invention relates to a process for producing a membrane for separating a liquid and/or gas mixture and in particular to a process for producing a membrane for separating the mixture, which is used for separation of a liquid and/or gas mixture by pervaporation, vapor permeation etc.
2. Description of the Related Art
Organic materials represented by polymeric materials such as polydimethylsiloxane and polyimide are used in membranes for separating liquid or gas mixtures, but there remain problems with thermal resistance and durability as well as selectivity and permeation rate in separation.
In recent years, separation membranes using inorganic materials have been studied to solve these problems of organic materials, among which zeolite membranes particularly attract attention. Among these zeolite membranes developed so far, there are known an NaA-type zeolite membrane obtained by subjecting an aqueous mixture containing a silica source and an alkali metal source to hydrothermal synthesis in the presence of an alumina porous support (Japanese Patent No. 2,501,825) and an A-type zeolite membrane deposited on a porous support (Laid-open Japanese Patent Publication No. Hei 8-318,141).
However, the NaA-type zeolite membrane, though being superior in mechanical strength, thermal resistance and water-selective permeability on pervaporation of a water/organic solvent system, is sensitive to acid, and when a trace acid is contained as an impurity in a mixture, the NaA-type zeolite membrane is deteriorated, so the pre-treatment of the mixture is required or the application of the membrane must be abandoned. Further, a separation membrane having the A-type zeolite membrane deposited possesses high water-selective permeability and is effective for separation of a water-ethanol mixture, but there is the problem of significant deterioration with acid.
The object of the present invention is to provide a membrane for separating a mixture, which can efficiently separate a liquid or gas mixture and is highly resistant to acid and alkali, thus solving the drawbacks of the conventional separation membranes described above.